A memory liquid crystal, which is capable of exhibiting a plurality of optical states, has a characteristic (a memory characteristic) such that it continues to retain a particular state even if a voltage is not applied to it. When such a memory liquid crystal is used in a liquid crystal display apparatus, the apparatus can be controlled to continue to display a particular image without requiring application of a voltage. In a display panel using a memory liquid crystal such as a ferroelectric liquid crystal, it is know to utilize the memory characteristic and perform control in such a manner as to drive scanning electrodes only for portions where the display needs to be updated but not to drive scanning electrodes for portions where the display need not be updated (for an example, see patent document 1).
It is also known to provide a transflective liquid crystal display apparatus that can operate in both reflective and transmissive display modes (for an example, see patent document 2). The transflective liquid crystal display apparatus includes a pair of substrates provided, therebetween, with a twisted nematic liquid crystal (TN liquid crystal) which operates to rotate the plane of polarization of incident light through 90 degrees, a polarizer mounted on one of the substrates, a reflective polarizer, having a reflection axis and a transmission axis, mounted on the other substrate, a semi-transmitting absorbing layer provided on the outer side of the reflective polarizer, and an auxiliary light source mounted on the outer side of the semi-transmitting absorbing layer.
In the transflective liquid crystal display apparatus, when the polarizers are arranged so that a dark display state is produced in an ON state in which a voltage of H level is applied to the TN liquid crystal (the TN liquid crystal is in the transmissive state) in the reflective display mode effected with the auxiliary light source turned off, then a bright display state will be produced in the ON state in which the voltage of H level is applied to the TN liquid crystal (the TN liquid crystal is in the transmissive state) when the transmissive display mode is effected by turning on the auxiliary light source. This is because, when the TN liquid crystal is set in the transmissive state with the auxiliary light source turned off, the display appears dark as the surface color of the turned off auxiliary light source is observed by the viewer, while when the TN liquid crystal is set in the transmissive state with the auxiliary light source turned on, the display appears bright as the light from the auxiliary light source is observed by the viewer. That is, the problem is that even if the voltage of the same level is applied to the TN liquid crystal, the dark display becomes reversed depending on the ON/OFF of the auxiliary light source. Therefore, to prevent the reversal of the dark display, it has been practiced in the prior art to switch the voltage to be applied to the TN liquid crystal (for example, from H level to L level).
Patent document 1: Japanese Unexamined Patent Publication No. H02-131286 (pages 11 and 12 and FIG. 12)
Patent document 2: Japanese Patent Publication No. 3485541